Preparation of binders for coatings, thermosetting coating compositions and their use

ABSTRACT

The preparation of water-thinnable thermosetting resin binder compositions for coatings is described wherein a polyglycidyl ether prepared by reacting a multifunctional polyglycidyl ether with a monofunctional phenol is reacted with a dicarboxylic acid in the presence of an esterification catalyst.

This is a division of application Ser. No. 694,738, filed Jan. 25, 1985now U.S. Pat. No. 4,614,775 issued Sept. 30, 1986.

FIELD OF THE INVENTION

This invention relates to a process for the preparation ofwater-thinnable curable binders for coatings, to binders prepared by theprocess, to aqueous thermosetting coating compositions containing thebinders and to the use of such compositions in coating articles.

BACKGROUND OF THE INVENTION

U.S. Pat. No. 4,246,089 discloses a glycidyl ether having on averageless than one epoxy group per molecule, which is the reaction product ofa bisphenol-A-derived diglycidyl ether and an alkyl phenol, e.g., nonylphenol, in molar ratio in the range 1:1.1 to 1:1.9; and the use of sucha glycidyl ether in preparing a graft copolymer based on anacrylic-amine backbone. Such graft copolymers are disclosed ascomponents of thermosetting coating compositions, e.g., forelectrocoating of vehicle bodies by cathodic electrodeposition.

U.S. Pat. No. 4,066,525 discloses the preparation of resinous bindermaterials containing substantially no residual epoxy groups by reactionof a bisphenol-A-derived diglycidyl ether with a phenol, e.g., nonylphenol, or with a mixture of a phenol and an amino alcohol, e.g.,diethanolamine. The resinous binder materials are used in thermosettingcoating compositions for electrocoating of applicances by cathodicelectrodeposition.

SUMMARY OF THE INVENTION

This invention is directed to a process for the preparation of awater-thinnable curable binder for coatings which comprises reactingtogether at a temperature in the range of from 60° to 170° C. and in thepresence of an esterification catalyst, a polyglycidyl ether which isthe reaction product of a multifunctional polyglycidyl ether and amonofunctional phenol, having 1 to 2 residual epoxy groups, adicarboxylic acid and optionally a diglycidyl ether to provide awater-thinnable binder having an acid value in the range of at least 20mg KOH/g and a content of incorporated monofunctional phenol in therange of from 5 to 40%w; to binders prepared by the process;thermosetting coating compositions containing them; and to the use ofsuch compositions in the electrodeposition coating of articles.

DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention is particularly directed to the preparation ofstable-water-thinnable binders which comprises reacting a polyglycidylether, which is the reaction product of a multifunctional polyglycidylether and an alkyl phenol, with a dicarboxylic acid, to produce curedcoatings having surprisingly enhanced flow and low porosity from saidstable thermosetting coating compositions. Accordingly, the presentinvention is therefore directed to a process for the preparation of anessentially epoxy-free, carboxyl group-containing water-thinnablecurable binder for coatings which comprises reacting together at atemperature in the range of from 60° to 170° C. and in the presence ofan esterification catalyst (a) a polyglycidyl ether having on average nepoxy groups per molecule, where 1<n≦2, which comprises the reactionproduct of a multifunctional polyglycidyl ether having on average xepoxy groups per molecule, where x>2, with (x-n) mol of a monofunctionalphenol per mol of the multifunctional polyglycicyl ether and (b) adicarboxylic acid.

The multifunctional polyglycidyl ether may conveniently be apolyglycidyl ether prepared by reaction of a polyhydric phenol having aphenolic hydroxyl functionality greater than 2, with an epihalohydrin,preferably epichlorohydrin, in the presence of a hydrogen halideacceptor, e.g., an alkali metal hydroxide.

Examples of suitable such polyhydric phenols are novolac resins ofgeneral formula ##STR1## wherein R represents an alkylene, e.g., CH₂,group, R¹ represents an alkyl group, e.g., a methyl, p-t-butyl, octyl ornonyl group, q and p are numbers having average values 0<q≦6 and 0≦p≦2,or of general formula, ##STR2## wherein R² represents an alkylene, e.g.,CH₂, group, R³ represents an alkylene, e.g., CH₂ or C(CH₃)2 group, acarbonyl group, an oxygen or sulfur atom and q' is a number having anaverage value in the range 0 to 2.

Other examples of suitable polyhydric polynuclear phenols are1,1-2,2-tetra(4-hydroxyphenyl)ethane and the tetraphenol derived fromdiphenolic acid having the general formula ##STR3## wherein R⁴represents the residue of a diol. Polyglycidyl ethers derived frompolyhydric phenols of formulae I, II and III are known and aredescribed, together with processes for their preparation. See, forexample, U.S. Pat. No. 2,844,553.

Preferably, the multifunctional polyglycidyl ether is an epoxy novolacresin wherein x is greater than 2 and is in the range from 2 to 6, andmore preferably x is in the range from 3 to 4.

Advantageously the epoxy novolac resin is derived from a novolac offormula I wherein R is CH₂, q is 1 to 2 and p is 0 to 1 or a bisphenolnovolac of formula II wherein R² is CH₂, R³ is C(CH₃)₂ and q' is 0.

Preferably n is in the range of from about 1.3 to about 2.

The monofunctional phenol may be a single phenol or a mixture ofphenols. For example the phenol may conveniently be phenol optionallysubstituted by one or more of one or more substituents selected fromC₁₋₁₆ alkyl, C₃₋₁₆ alkenyl, C₁₋₄ hydroxyalkyl, C₂₋₁₃ alkoxycarbonyl andC₁₋₁₆ alkoxy groups. Examples of such compounds include phenol, thecresols, salicyl alcohol, 2-allyl phenol, 2,4,6-triallyl phenol,dimethyl phenol, 4-hydroxymethyl-2,6-dimethyl phenol, 2-hydroxyphenethylalcohol, 4-hydroxybenzyl alcohol and ethyl 4-hydroxybenzoate. Preferablythe monofunctional phenol is phenol substituted in the para-position bya C4-12 alkyl substituent. Examples of such alkyl substituents includen-, iso- and t-butyl, n- and iso-octyl, n-and iso-nonyl and n- andiso-dodecyl groups Branched alkyl substituents are particularlysuitable. 2(1,1-3,3-tetramethyl-butyl)phenol has been found to be a verysuitable monofunctional phenol.

The polyglycidyl ethers may conveniently be prepared by reacting themultifunctional polyglycidyl ether with the monofunctional phenol at atemperature in the range from about 120° to 180° C. in the presence ofan acid or base catalyst.

Preferably, the reaction is at a temperature from about 130° to 150° C.

The acid or base catalyst may be, for example, a tertiary amine, aquaternary ammonium or phosphonium salt or an alkali metal hydroxide orcarbonate, or sulfuric acid.

The tertiary amine may be, for example, triethanolamine, benzyldimethylamine or 2-dimethylamino-2-methyl-1-propanol. Quaternaryammonium salts, e.g., tertiary ammonium chloride, are preferredcatalysts.

Tertiary amine catalysts are preferably used in amounts from 0.1 to 1%wof reactants and quaternary ammonium salts are preferably employed inamounts from 0.005 to 0.2%w of reactants.

The dicarboxylic acid may conveniently be an aliphatic dicarboxylicacid. Examples of such compounds include succinic acid, maleic acid,glutaric acid, itaconic acid, adipic acid, pimelic acid, suberic acid,azelaic acid, sebacic acid, 1,12-dodecanedioic acid, dodecenyl succinicacid, noneyl succinic acid, dimerized fatty acid.

Another class of dicarboxylic acids which may conveniently be used arethose obtained by partial esterification or amidation of apolycarboxylic acid or a polycarboxylic acid anhydride. Examples of suchcompounds include the monoalkyl esters of trimellitic anhydride and thedialkylesters of pyromellitic anhydride. Preferably, these alkyl estersare derived from primary alkanols having at least 6 carbon atoms.Further examples of these ester type dicarboxylic acids can, forexample, be obtained by partial esterification or amidation of thereaction product of 2 moles of trimellitic anhydride and 1 mole of analiphatic diol.

Preferred dicarboxylic acids are those having water solubility below 0.3g/100 g water of 20° C. Azelaic acid and sebacic acid have been found tobe very suitable dicarboxylic acids.

It will be appreciated by those skilled in the art that the ultimatereaction product of the reaction between the dicarboxylic acid and thepolyglycidyl ether will be an essentially linear molecule. In order tobe Potentially water soluble or water dispersible after neutralizationand furthermore in order to be essentially free of epoxy groups thismolecule should have on average a carboxyl group at each end and an acidvalue in the range of at least 20 mg KOH/g. To this end the dicarboxylicacid and the glycidyl ether compounds should be reacted in such amountsthat there is an excess of 2 equivalents of acid over the totalequivalents of epoxy. When the water-thinnable binder is used incompositions which will be applied by an electrodeposition process, theacid value should not be too high for process technical reasons. Inother words, for such an application it is preferred that the acid valueof the water soluble binder be in the range of from about 20 to 80 mgKOH/g. Most preferably, the acid value should be in the range of from 30to 50 mg KOH/g.

If desired a quantity of a known liquid or solid diglycidyl ether, maybe included with the above polyglycidyl ether in the reaction with thedicarboxylic acid in the above process for preparing a water-thinnablebinder.

The diglycidyl ether is preferably a diglycidyl ether of a dihydricphenol, e.g, a bisphenol. Conveniently the diglycidyl ether is adiglycidyl ether of 2,2-bis(4-hydroxyphenyl)propane having a weight perepoxide (WPE) in the range 170 g to 1500 g. Preferably, the diglycidylether has a WPE in the range from about 400 g to 1100 g. Examples ofvery suitable diglycidyl ethers of 2,2-bis(4-hydroxyphenyl)propaneinclude the commercially available EPON® Resin 1001 (WPE of about 450 gto 500 g) and EPON® Resin 3003 (WPE of about 725 g to 825 g).

The amount of diglycidyl ether which can optionally be co-reacted withthe dicarboxylic acid and the polyglycidyl ether is determined by theamount of monofunctional phenol which has to be incorporated in order toachieve the aforementioned improvements. Coatings with improved flow andreduced porosity can be obtained when the amount of monofunctionalphenol incorporated in the ultimate water-thinnable binder is in therange of from 5 to 40%w. Preferably the amount of monofunctional phenolis in the range of from 10°to 25%w.

In the preparation of the water-thinnable binder, which is conducted ata temperature in the range of 60° to 170° C., reaction between aliphatichydroxyl groups and epoxy groups or carboxyl groups should be avoided.This may be achieved by employing a tertiary amine, e.g.,2-dimethylamino-2-methyl-1-propanol, as catalyst for the reaction ofepoxy groups with carboxyl groups.

Tertiary amine catalysts are preferably used in amounts from about 0.1to 1%w of reactants. Preferably, the reaction between the dicarboxylicacid and the glycidyl ether is conducted at a temperature in the rangeof from about 100° to 150° C.

The invention further provides binders prepared by the process of theinvention and also aqueous thermosetting coating compositions comprising(A) a binder prepared by the process of the invention and (B) acrosslinking compound in a solids weight ratio A:B in the range fromabout 95:5 to 60:40, preferably 85:15 to 65:35, more preferably, 85:15to 75:25. The thermosetting coating compositions are prepared bycombining the binder with the cross-linking compound before or afterneutralization. The invention also specifically provides use of athermosetting coating composition of the invention in electrodepositionof articles (anodic electrodeposition).

Preferred crosslinking compounds, for addition to the binder compoundsbefore of after neutralization, are water-soluble crosslinking agents ofthe aminoplast type, such as alkoxylated reaction products offormaldehyde with melamine or benzoguanamine.

Other crosslinking compounds include urea-formaldehyde resins,phenol-formaldehyde resins, and block polyisocyanates.

Pigments, fillers, dispersing agents, and other components known in theart of paint formulation may further be added. Addition of small amounts(up to 1%w) of non-ionic surfactant may be useful for furtherstabilization of aqueous compositions or improvement of the wettingduring application. Co-solvents, such as 2-n-butoxyethanol and,especially, 2-n-hexyloxyethanol, may advantageously be included. Thewater for use in the aqueous compositions is preferably purified, suchas by distillation or demineralization. The water-dilutable compositionsmay be applied by a variety of methods known in the art, onto a varietyof substrates, in particular metals such as bare steel, phosphatedsteel, chromate-treated steel, zinc, tin plate (for can coating), andaluminum (also e.g. for can coating), to produce cured coatings ofdesirable thickness, from 2 micrometers upwards up to in general 40micrometers.

Curing can be performed by stoving, for example, at temperatures from150° to 220° C., with curing times varying from 2 to 30 minutes.

The thermosetting coating compositions may generally be applied byelectrodeposition and other methods such as spraying or dipping, and areparticularly suitable for coating cans by electrodeposition. Thoseskilled in the art will appreciate the need to select compounds whichare approvable by regulatory authorities when food or beverage cans areto be coated.

The invention will be further understood from the following illustrativeexamples, in which parts and percentages are by weight, unless otherwiseindicated, and various terms are defined as follows:

"Multifunctional polyether A" is a semi-solid multifunctional epoxynovolac resin of average molecular weight 665 g, containing on average3.5 epoxy groups per molecule.

"Polyether D" is a solid diglycidyl ether of2,2-bis(4-hydroxyphenyl)propane of a WPE of about 485, containing onaverage 1.85 epoxy groups per molecule.

CYMEL 1141 (trademark) is a highly alkylated melamine-formaldehydecuring resin containing methoxy and isobutoxy substituents and acidicchelating groups, 85% solids in isobutanol, AV 22±3 mg KOH/g.

EXAMPLE 1 Adduct for use as anodic electrodeposition binder (a)Preparation of reaction product of multifunctional polyglycidyl etherwith monofunctional phenol

Multifunctional polyether A (665 g, 1 mol, 3.5 epoxy equivalents) andp-(1.1.3.3-tetramethyl-butyl)phenol (309 g, 1.5 mol) were heated withstirring to 140° C. When the mixture was homogeneous, a 50%w aqueoussolution of tetramethylammonium chloride (1 g) was added and the mixturewas maintained at 140°-150° C. until the reaction was complete (4hours). The resulting product having an epoxy content of 2.05 meq/gsolids (average 2 epoxy equivalents per molecule) and a residualphenolic hydroxyl content of 0.01 meq/g solids.

(b) Preparation of adduct for use as anodic electrodeposition binder

Polyether D (1940 g, 4 epoxy equivalents) was added to the reactionproduct of step (a) and heated at 140° C. until the mixture washomogeneous. Subsequently azelaic acid (752 g, 4 mol, 8 acidequivalents) and 2-dimethylamino-2-methyl-1-propanol (5 g) were addedand the mixture was heated to 140°-150° C. with stirring and kept atthis temperature for a further 6 hours, until the reaction was complete.The resulting binder, which had an epoxy content of 0.02 meq/g solidsand an acid value of 31 mg KOH/g, was allowed to cool to 120° C.whereupon it was diluted with 2-n-butoxyethanol (916 g), resulting in aclear viscous solution having a solids content of 80%w; the ultimatebinder had an incorporated alkyphenol content of 8.4%w.

EXAMPLE 2 Adduct for use as anodic electrodeposition binder

Twice the amount of the reaction product of Example 1(a) (i.e. 1948 g, 4epoxy equivalents), 970 g of polyether D (2 epoxy equivalents) and 752 gazelaic acid (4 mol, 8 acid equivalents) were reacted in the presence of2-dimethylamino-2-methyl-1-propanol following the procedure described inExample 1(a). 987 g of 2-n-butoxyethanol was used to dilute theresulting binder (acid value 32 mg KOH/g), which resulted in a clearviscous solution having a solids content of 78.8%w.

The ultimate reaction product had an incorporated alkylphenol content of16.8%w.

EXAMPLE 3 Adduct for use as anodic electrodeposition binder (a)Preparation of reaction product of multifunctional polyglycidyl etherwith monofunctional phenol

Multifunctional polyether A (665 g, 1 mol, 3.5 epoxy equivalents) andp-tertiary butyl phenol (300 g, 2 mol) were heated with stirring to 140°C. When the mixture was homogeneous, a 50%w aqueous solution oftetramethylammonium chloride (1 g) was added and the mixture wasmaintained at 140°-150° C. until the reaction was complete (4 hours).The resulting product had an epoxy content of 1.57 meq/g solids (average1.51 epoxy equivalents per molecule).

(b) Preparation of adduct for use as anodic electrodeposition binder

The reaction product of 3(a) (965 g, 1.5 epoxy equivalents) was reactedwith sebacic acid (253 g, 1.25 mol, 2.5 acid equivalents) in thepresence of 2.5 g 2-dimethylamino-2-methyl-1-propanol following theprocedure described in Example 1(b). The ultimate binder (acid value 48mg KOH/g) was diluted with 304 g of 2-n-butoxyethanol to give a clearviscous solution having a solids content of 80%w. The incorporatedalkylphenol content of the ultimate binder was 24.6%w.

EXAMPLE A (comparative) Adduct for use as anodic electrodepositionbinder Polyether D (1940 g, 4 epoxy equivalents) was reacted withazelaic acid (564 g, 3 mol, 6 acid equivalents) in the presence of 6 gof 2-dimethylamino-2-methyl-1-propanol under the conditions as describedin Example 1(b) to arrive at a binder having an acid value of 43.8 mgKOH/g solids and no residual epoxy functionality. This product wasdiluted with 628 g of 2-n-butoxyethanol to arrive at a viscous solutionhaving a solids content of 79.9% w. EXAMPLE B (comparative) Adduct foruse as anodic electrodeposition binder (1) Preparation of reactionproduct of multifunctional polyglycidyl ether with monofunctional phenol

665 g of Multifunctional polyether A (1 mol, 3.5 epoxy equivalents) wasreacted with 412 g of p-(1,1-3,3-tetramethylbutyl)phenol (2 mol)resulting in a reaction having an epoxy content of 1.35 meq/g (average1.46 epoxy equivalents per molecule) and a phenolic hydroxyl contentlower than 0.01 meq/g. This product was diluted with 555 g of2-n-butoxyethanol to arrive at a solution having a solids content of 66%w.

(2) Preparation of adduct for use as anodic electrodeposition binder

Glycine (54.7 g, 0.73 mol), water (150 g) and potassium hydroxide (46.9g, 0.73 mol) were heated with stirring to 100° C. The reaction productof step (1) (1633 g of a 66% w solution in 2-n-butoxyethanol, 1 molpolyether product) was added slowly, with stirring over a period of 4hours while maintaining the temperature of 100° C. Upon completion ofthe addition the mixture was stirred at 100°-110° C. for a further hour.The final product was a clear viscous solution, in which no epoxy groupscould be detected. Subsequently this solution in 2-n-butoxyethanol wasdiluted with the addition of 5848 g demineralized water with stirring toarrive at a solution having a solids content of 15% w.

To 1000 g of this solution was added 80 g of an ion exchange resin,"Dualite C-26 TR" (registered trade name),--a sulfonatedstyrene-divinylbenzene copolymer containing 8% crosslinks--which hadpreviously been neutralized with 2-dimethylamino-2-methyl-1-propanol, toresult in an ion exchange resin having a loading of 1.9 meq2-dimethylamino-2-methyl-1-propanol/g of wet resin. The mixture wasstirred at room temperature for 6 hours whereupon the spent ion exchangeresin was filtered off and the same procedure repeated with a further 80g of the 2-dimethylamino-2-methyl-1-propanol containing ion exchangeresin.

The final ion exchanged solution was clear, had a solids content of14.5% w and contained less than 2 ppm potassium on solution.

EXAMPLES 4-6 Anodic electrodeposition composition

The adducts of Examples 1-3, in the form of the respective solutions in2-n-butoxyethanol obtained in those Examples, were blended with CYMEL1141 in binder solids to CYMEL 1141 weight ratio 70:30 and subsequentlyfurther diluted with 2-n-hexyloxyethanol, to arrive at solutions havinga solids content of 76%w, neutralized with a 90% equivalent amount of2-dimethylamino-2-methyl-1-propanol and diluted by gradual addition ofdemineralized water to a final solids content of 15.5% w.

EXAMPLE C (comparative) Anodic electrodeposition composition

The adduct of Example A, in the form of its solution in2-n-butoxyethanol, as obtained in said Example was processed followingthe procedure of Examples 4-6.

EXAMPLE D (comparative) Anodic electrodeposition composition

The solution of the ion exchanged adduct as obtained in Example B wasblended with CYMEL 1141 in a binder solids to CYMEL 1141 weight ratio70:30 and was stirred at room temperature for 48 hours before use.

EXAMPLES 7-9 Use of anodic electrodeposition compositions in can coating

The coating compositions of Examples 4 to 6 were used to coat 330 mltin-plate cans by anodic electrodeposition. The can formed the anode ofan electrodeposition cell, the cathode being a stainless steel memberinserted within the can at a substantially uniform separation of 2millimeters from the can. A potential difference, which would resultafter baking in a coating weight per can in the range of 180 to 220 mgcorresponding with a dry film thickness in the range of 6 to 7 mm, wasapplied between the can and the cathode, for a total time of 400milliseconds. After electrodeposition the coated can was vigorouslyrinsed with demineralized water, and the coating was cured by stovingthe coated can for 5 minutes at 200° C.

After curing and measuring coating weight, porosity was tested by usingan electrolyte solution containing a red indicator (6.2 V for 30 sec).Subsequently the cans were filled with a second clear electrolytesolution. The areas of the can not covered by the coating, became red.Using this method it is easy to identify pores or other coating defects.

For comparative reasons similar experiments were conducted withcompositions of Examples C and D. Results are given in Table Ifollowing, in which solvent resistance is expressed in terms of "MEKrubs", i.e., the number of double rubs with amethylethylketone-moistened cloth necessary to remove the coatings,while the film appearance (flow) is expressed as a numerical ratingresulting from a visual assessment (5: smooth surface, excellent flow,no defects, 4: orange-peel type surface, 3: orange-peel type surface andfew bubbles and/or pinholes, 2: many bubbles and/or pinholes).

The sterilization resistance of the coatings was determined by exposureto water at 121° C. for 90 minutes and rated according to a numericalscale ranging from 5: no blushing to 0: very heavy blushing.

                                      TABLE I                                     __________________________________________________________________________                Alkylphenol                                                                          Application                                                                         Coating                                                                            Film                                                        incorporated                                                                         voltage                                                                             weight                                                                             appearance                                                                          Porosity                                                                           Mek Sterilization                    Example                                                                            Composition                                                                          (% w)  (V)   (mg) (flow)                                                                              (mA) rubs                                                                              resistance                       __________________________________________________________________________    4    4      8.4     90   210  4-5   1.0  >100                                                                              5                                5    5      16.8   100   215  5     0.2  >100                                                                              5                                6    6      24.6   100   205  5     0.8  >100                                                                              4-5                              Comparative C                                                                             0      110   195  5     70   >100                                                                              4-5                              Comparative D                                                                             35.5    75   210  3     115  >100                                                                              4-5                              __________________________________________________________________________

The use of the binder composition of Examples 4 to 6 results in coatingswhich all exhibit excellent properties, and significantly better flowand/or reduced porosity compared to those of Examples C and D.

What is claimed is:
 1. An aqueous thermosetting coating compositioncomprising (A) a water-thinnable curable binder prepared by a processcomprising the steps of: reacting together at a temperature from about60 to about 170° C. and in the presence of an esterification cata-ystwhich promotes the selective reaction of epoxy groups with carboxylgroups (a) a poly glycidyl ether having, on average, n epoxy groups permolecule, where 1≦n<2, which comprises the reaction product of amultifunctional polyglycidyl ether having, on average, x epoxy groupsper molecule, where x>2, with (x-n) mol of a monofunctional phenol permol of the multi functional polyglycidyl ether and (b) a dicarboxylicacid in an amount and under conditions effective for reactingessentially all the n epoxy groups per molecule with the dicarboxylicacid and producing a reaction product of (a) and (b) having an acidvalue in the range of about 20 to about 80 mg KOH/g and (B) acrosslinking compound present in an amount such that the solids weightratio A:B is from about 95:5 to 60:40.
 2. The composition of claim 1 inwhich the crosslinking compound is selected from urea-formaldehyderesins, water-soluble aminoplasts, phenol-formaldehyde resins and blockpolyisocyanates.
 3. The composition of claim 1 in which the crosslinkingcompound is a melamine-formaldehyde resin.
 4. The composition of claim 1in which the solids weight ratio A:B is in the range of from about 85:15to about 65-35.
 5. The composition of claim 1 in which, in thepolyglycidyl ether, 1.3≦n≦2.
 6. The composition of claim 1 in which thepolyglycidyl ether is derived from a multifunctional polyglycidyl etherwhich is an epoxy novolac resin wherein 3≦x≦4.
 7. The composition ofclaim 1 in which the monofunctional phenol from which the polyglycidylether is derived is phenol substituted in the para position by a C₄ -C₁₂alkyl substituent.
 8. The composition of claim 1 in which thedicarboxylic acid has a water solubility below 0.3 g/100 g water at 20°C.
 9. The composition of claim 1 in which the dicarboxylic acid isreacted with a mixture of the polyglycidyl ether and a diglycidyl ether.10. The composition of claim 9 in which the diglycidyl ether is adiglycidyl ether of Z,2,2-bis(4-hydroxyphenyl)propane having a weightper epoxide of about 70 g to 1500 g.
 11. The composition of claim 1 inwhich the water-thinnable curable binder has a content of incorporatedmonofunctional phenol from about 10 to 25 weight percent.
 12. Thecomposition of claim 1 in which the water-thinnable curable binder hasan acid value of from about 30 to 50 mg KOH/g.
 13. The composition ofclaim 1 in which the esterification catalyst is a tertiary amine.